A boy whose Kiwi mother refused to allow doctors to treat him for cancer has had successful brain surgery, but she is continuing to argue against radiotherapy.

Neon Roberts' mother made headlines across the UK after refusing to have him treated for fear of the side effects of radiotherapy.

The surgery reportedly went well, the court has now heard, but Roberts is refusing to let doctors treat him with anti-sickness drugs, according to the Daily Mail.

Sally Roberts, a former DJ from Auckland, went on the run with her seven-year-old son for four days before British police eventually caught her and brought them back.

Earlier this week, she lost the battle to prevent her cancer stricken boy from receiving more treatment, with a judge in the United Kingdom ordering it.

The Daily Mail reported she failed overnight in her attempt to get legal proceedings surrounding whether Neon can receive radiotherapy adjourned after the High Court heard her expert could not even spell the form of the disease he is suffering from.

Roberts originally wanted any operation on her son delayed until more doctors had been consulted about the need for further surgery.

The Family Division of the High Court in England was told by doctors that Neon needed further brain surgery before radiotherapy could begin and without it, he would die.

Neon has already had brain surgery to remove a tumour and was expected to have radiotherapy in the weeks after before his mother took him on the run.

At the weekend, Roberts and her estranged husband Ben Roberts received news that Neon's cancer had returned.

MRI scans showed a mass, about 1cm in diameter, had grown.

According to the Daily Mail, Roberts had initially consented to Neon having the radiotherapy but changed her mind just before the hearing.